The present invention relates to systems and devices for monitoring patients in a healthcare facility and particularly to patient monitoring systems that allow the patient to ambulate through a care unit in the facility.
Most patient monitoring systems that permit patients to ambulate through a care unit use telemetry-based communication schemes. In one common form, the patient wears a telemetry transmitter attached to the patient using ECG electrodes. The telemetry transmitter acquires an ECG signal, conducts a nominal amount of filtering on the ECG signal, and transmits a telemetry data signal to an antenna array, typically located in the ceiling of the care unit. The telemetry signal is conducted through the antenna array to a telemetry receiver, which in turn, is connected to a central station that analyzes and displays the ECG information for viewing and evaluation by the clinicians staffing the care units.
Existing medical telemetry systems are regulated by the Federal Communications Commission (xe2x80x9cFCCxe2x80x9d) and are required to use VHF (very high frequency) and UHF (ultra high frequency) radio-frequency (xe2x80x9cRFxe2x80x9d) bands for their wireless data links. Presently, it is necessary to install two separate telemetry infrastructures or systems to utilize both of these bands. Of course, installing two systems increases the cost of patient monitoring. Proposed changes in FCC regulations will provide a new band (the L-band) in the RF spectrum for medical telemetry systems. While the addition of the new band will provide new capacity for telemetry systems and help reduce interference with other RF signals, operating in the new band with current technology would require an additional and separate telemetry infrastructure. However, if L-band telemetry systems could be implemented without additional infrastructure, significant cost savings could be realized.
Accordingly, the present invention provides a dual band telemetry system that is capable of receiving both UHF and L-band signals. The architecture of the system permits the detection and processing of L-band and UHF signals with a common receiver and antenna system, thereby eliminating costly, redundant infrastructure that would otherwise be required.
The system includes an antenna system having a first antenna tuned to receive a signal having a frequency in a first frequency band, a second antenna tuned to receive a signal having a frequency in a second frequency band, a down converter for producing a frequency translation signal, and a mixer coupled to the second antenna and the down converter. The mixer combines the signal received by the second antenna with the frequency translation signal to produce a signal having a frequency in the first frequency band. In other words, the mixer converts the signal received by the second antenna to a signal in the first frequency band. A combiner coupled to the mixer and the first antenna combines the signal generated by the mixer with the signal received by the first antenna. The combined signals are then delivered to a receiver station or subsystem designed to receive signals in the first frequency band.
One advantage of the present invention is that it eliminates the need to provide a receiver subsystem capable of processing signals in the second frequency band. The signal received by the second antenna is converted to a signal in the first frequency band and, thus, may be processed by the same receiver subsystem that processes signals from the first antenna.
Preferably, the dual band telemetry system of the present invention is designed to operate with RF signals. In particular, the first antenna is designed to receive UHF signals and the second antenna is designed to receive L-band signals. The first antenna is designed to receive signals in a particular channel within the UHF band and the signals from the second antenna are converted to a second channel in the UHF band before detection at the receiver station.
The down converter is designed so that the frequency of the translation signal may be selected so that the converted signal produced by the mixer falls within the second channel in the first frequency. The frequency of the second channel depends on factors such as avoiding interference with other RF signals including the signal from the first antenna and local UHF signals from television broadcasts. To set an appropriate frequency for the translation signal, the down converter uses an oscillator, a synthesizer, and a filter coupled in a series loop (i.e., the components form a phase-lock loop). The synthesizer is programmed through a microprocessor that can receive input from a technician, administrator, or similar person to adjust the frequency. The synthesizer derives its frequency reference from a temperature controlled oscillator to compensate for temperature changes.
The antenna system is designed to work with telemetry transmitters worn by patients in a care unit, a receiver subsystem, and a central station. The transmitters acquire patient data and transmit that data at a predetermined frequency. In its simplest form, the system operates with one telemetry transmitter that operates in the first frequency band and a second transmitter that operates in the second frequency band. The signals sent by the telemetry transmitters are received by the first and second antennas and the signal from the second antenna is converted as described above. The signal from the first antenna and the converted signal are then relayed to the receiver subsystem which in turn delivers the signals to a central station. The patient data is collected and analyzed at the central station.